Transmission power control in a radio communication system

ABSTRACT

The present invention relates to a method in a communication system. The system comprises a controller arranged to control transmission power of stations, a first station and a second station, the controller being arranged to provide the first station with a target for use in control of the transmission power of the second station, monitoring means, and means for preventing use of a target for the transmission parameter that exceeds a limit value. The controller provides the first station with the target and the first station adjusts the transmission power of the second station on basis of the target. A predefined condition is monitored, and upon occurrence of the predefined condition, use of a target for the transmission parameter exceeding a limit value for the target for the transmission parameter is prevented.

FIELD OF THE INVENTION PRIORITY CLAIM

This is a national stage of PCT application No. PCT/EP00/09105, filed onSep. 14, 2000. Priority is claimed on that application, and on patentapplication No. 9921989.1 filed in Great Britain on Sep. 16, 1999.

The present invention relates to power control in a communicationsystem, and in particular, but not exclusively, to power control of astation of the communication system in a power limitation situation.

BACKGROUND OF THE INVENTION

In a mobile telecommunication system, such as CDMA (Code DivisionMultiple Access) or WCDMA (Wide-band CDMA) or TDMA (Time divisionMultiple Access) system, transmission power levels between a base(transceiver) station (BS) and a mobile station (MS) associated withsaid base station can be continuously adjusted during an ongoingconnection between the base station and the mobile station. This is donein order to provide a sufficient quality for the transmission in variousconditions. To reduce power consumption and interference it is alsopreferred to keep the required transmission power levels as low aspossible at the same time. By means of this it is possible to avoid“wasting” any network resources and power resources, and to enable asgreat a number of mobile stations as possible to communicatesimultaneously with the base station having only limited powerresources. The power resources of the base station are limited both intransmission (downlink) and receiving (uplink) directions.

In the uplink the limitation means that a base station cannot receiveand process more than a predefined number of connections from mobilestations. The uplink direction can be limited by increased qualityrequirements, e.g. in a situation in which a great number of mobilestations is communicating via the base station and request for a highertransmission quality. If the power levels are increased in the cell inorder to improve the quality, this increases interference in the uplink.Therefore, in addition to the incapability of the base station toreceive more than a limited amount of transmission power from the mobilestations, too high transmission powers from the mobile stations maycause too high interference to the radio traffic within the cell and/orhave an adverse influence to the overall performance of the basestation.

One power control mechanism is based on power control (PC) commandstransmitted between two stations to cause the other station to alter oradjust or change its transmission power. The PC commands can betransmitted e.g. in a WCDMA closed loop functioning between the BS andthe MS. The closed loop PC (CLPC) commands can be sent both in theuplink (towards the base station) and in the downlink (towards themobile station), whereafter the BS or the MS will process the receivedcommand and reduce/increase its transmission power towards the receivingstation accordingly.

The power control between the stations, such as the closed loop PC, canbe controlled by another power control command generated by a controllerof the communication system. For example, in the currently proposedWCDMA system it is envisaged that an outer loop power control (OLPC)command generated by a radio network controller (RNC) of the WCDMAsystem will attempt to set the connection quality target of a physicalconnection between the BS and MS to be such that a required FER (FrameError Ratio) target or BER (Bit Error Ratio) target or any other similartarget of the connection is met with a minimal connection qualitytarget. The closed loop power control command is then adjusted at thebase station in accordance with the outer loop power control commandreceived from the controller. The connection quality target maysometimes be referred to as a connection setpoint.

The connection quality target or setpoint can be announced e.g. by meansof so called Eb/No (Signalling Energy/Noise) target or SIR (Signal toInterference Ratio) target or desired signal level target or a similarparameter indicating a quality measure which can be estimated for theconnection. The relationship is such that the connection quality target(e.g. the SIR target) has to be set such that the FER or the BER orsimilar parameter of the connection remains at an appropriate level. Theactual connection quality value (e.g. SIR) is then controlled inaccordance with the target value, and one or several of used connectionparameters having influence to the quality of the connection shouldfollow any changes in the target value. In most cases it is sufficientif the transmission power is increased/decreased in order to meet thetarget value. The idea behind the arrangement is that by increasing theconnection quality target value the transmission power (or any otherappropriate transmission parameter having an influence over theconnection quality) will increase and thus the connection quality willincrease and the FER will improve.

However, if the appropriate target of the connection quality cannot bemet due to e.g. a power limitation situation the connection qualitytarget will start increasing, even though this rise in the connectionquality target will not help in causing a better connection between theMS and the BS. The power limitation condition at the BS can be causede.g. by an overload situation or a failure. If the power limitation isonly temporary the quality target will also be unnecessarily high oncethis condition has been removed. The temporary power limitation canoccur e.g. when too many mobile stations are trying to become connectedto one BS, e.g. when a bus or train with several mobile users suddenlyenters the radio coverage area of the base station. The power limitationmay also occur e.g. when the radio connection between the BS and one orseveral mobile stations weakens temporarily, for instance, the MS enterstemporarily a tunnel or cellar, which will cause a rapid rise in thetransmission powers. The failures causing a power limitation situationmay occur in the base station, elsewhere in the communication system orin the mobile stations. The power limitation situation may result in anexcessively high power levels within the cell until the quality targethas returned to its normal (nominal) level. In addition, an uncontrolledpower limitation situation (i.e. the powers of the mobile stations mayrise freely) will lead to a situation in which the mobile stationspositioned in the edge area of the cell start loose the connection i.e.the mobile stations “drop” from the cell. This leads to a decrease inthe size of the cell.

Earlier proposals to solve the problems caused by the power limitationsituation have been based on setting absolute limits on the values ofthe SIR targets. However, the absolute limits have to be relativelyloose due to the variations in the required quality target forsatisfactory quality of the communication. There has not been anyefficient means for rapidly preventing an excessive increase of thetarget or setpoint value in an overload or other sudden power limitationsituation. Instead, the target value has increased further as the targetis increased accordingly despite the fact that no more power isavailable or can be received. In addition, when the power limitationsituation is over, the recovery from the increased and unnecessarilyhigh target values may take some time.

SUMMARY OF THE INVENTION

The embodiments of the present invention aim to address one or severalof the above problems.

According to one aspect of the present invention, there is provided amethod in a communication system, said system comprising a controllerand a first station for communication with a second station withvariable transmission power over a radio connection, wherein thecontroller provides the first station with a target for a transmissionparameter of the radio connection and the first station adjusts thetransmission power of the second station on basis of the target,comprising: monitoring for a predefined condition; upon occurrence ofthe predefined condition, preventing use of a target for thetransmission parameter exceeding a limit value for the target for thetransmission parameter.

According to a more specific embodiment the use of a target for thetransmission parameter exceeding the limit value is prevented at thefirst station. The use of a target for the transmission parameterexceeding the limit value can also be prevented at the controller. Thelimit value may equal with the target for the transmission parameter inuse at the moment of detecting the predefined condition. The predefinedcondition may comprise a temporary power limitation situation at thefirst station, an overload situation at the first station or a failurein the communication system. The monitoring of the occurrence of thepredefined condition can be based on determination of the interferencepower of the radio connection.

According to a further embodiment a difference between the value of thetarget for the transmission parameter provided by the controller and thevalue of the target for the transmission parameter used for powercontrol by the first station is detected after the predefined conditionis over, whereafter the difference between the said two target values isreduced. The difference can be reduced based on history information ofthe target used for the power control prior the detection of thecondition. The difference between the said two target values can bereduced gradually.

According to another aspect of the present invention there is provided acommunication system, comprising: a controller arranged to controltransmission power of stations; a first station and a second stationcapable of providing a communication path therebetween, wherein thecontroller is arranged to provide the first station with a target foruse in control of the transmission power of the second station;monitoring means for monitoring for a predefined condition; and meansfor preventing use of a target for the transmission parameter exceedinga limit value for the target for the transmission parameter uponoccurrence of the predefined condition.

The communication system may comprise further detecting means fordetecting a difference between the target and the further target andrecovery means for reducing the difference after the predefinedcondition is over.

According to a still another aspect of the present invention there isprovided a station of a communication system, said station controllingtransmission power of a further station transmitting towards thestation, wherein the station is arranged to: receive a target for atransmission parameter provided by a controller of the communicationssystem for use in the control of transmission power of the furtherstation; monitor for a predefined condition; and upon occurrence of thepredefined condition, to prevent use of targets for the transmissionparameter exceeding a limit value for the target for the transmissionparameter.

The embodiments of the invention provide several advantages. Should apower limitation situation occur, the embodiments prevent the situationgetting even worse by preventing a unnecessary rise of the connectionquality target or similar parameter influencing the transmission powerin the cell. The powers in the cell may be limited in a level that stillcan be handled by the base station. The embodiments may also prevent anincrease in the interference in the cell. Since the embodiments enablepower resource situation within the cell to remain stable, it ispossible to prevent disconnection of the ongoing connections, or tolimit the disconnecting procedures to the connections having a lowestpriority. In addition, the embodiments provide a fast response to apower limitation situation without any excessive delays due to e.g.signalling between a base station and a network controller or severalcontrollers. In addition, the specific embodiments provide a controlledand “smooth” recovery procedure after the power limitation situation hasended.

BRIEF DESCRIPTION OF DRAWINGS

For better understanding of the present invention, reference will now bemade by way of example to the accompanying drawings in which:

FIG. 1 shows schematically a part of a communication system in which theinvention can be implemented;

FIG. 2 is a block diagram of the base station and the controller of thecommunication system of FIG. 1;

FIG. 3 illustrates schematically an embodiment of an outer loop powercontrol mechanism in an overload situation;

FIG. 4 illustrates schematically a further embodiment of an outer looppower control mechanism in an overload situation;

FIG. 5 is a table presenting an example of the operation of the presentinvention at the transceiver of the communication system;

FIG. 6 is a table presenting an example of the operation of the presentinvention at the controller of the communication system;

FIG. 7 is a flowchart illustrating the operation of an embodiment; and

FIG. 8 is a flowchart illustrating the operation of a furtherembodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a block diagram illustrating a context in which the presentinvention may be used. That is, a WCDMA system (Wideband CDMA) mobilecommunication system allows a plurality of mobile stations MS1, MS2, MS3to communicate with a base transceiver station (BS) 4 in a common cellover a radio interface via respective channels CH1, CH2, CH3. The basestation can sometimes be referred to as node B. In the CDMA basedsystems these channels are distinguished from one another by the use ofscrambling codes in a manner which is know per se. Communication betweenthe mobile stations 1–3 and the base station 4 may comprise any kind ofdata such as speech data, video data or other data. The power controlcommands between the mobile stations and the base station are handled bya closed loop power control mechanism.

The base station 4 is controlled by a controller 5 of the communicationsystem. In the CDMA terminology this controller is often referred to asa radio network controller (RNC). The general arrangement is such thatwhile the base station 4 controls the individual mobile stations 1–3 inits radio coverage area via the radio channels, the network controller 5functions as a “central” controller controlling several base stations.The mobile stations 1–3 can be controlled by the controller 5 throughthe base station 4.

In the currently proposed WCDMA system the base station 4 receivesappropriate control commands from the controller 5 via an outer loop(OL) power control (PC) mechanism. As response to the received commandsthe base station 4 proceeds accordingly to control the connections withindividual mobile stations 1–3 via the closed loop (CL) between therespective mobile station and the base station. According to onepossibility the commands may be transmitted in the closed loop in thefrequency of 1.5 kHz, and in the outer loop in the frequency of about 10to 100 Hz. However, it is noted that any other frequencies may be usedhere. The following description of the embodiments will concentrate inmore detail on the outer loop power control (OLPC) mechanism between thebase transceiver station 4 and the controller 5.

FIG. 2 shows in more detail a base station 4 and a radio networkcontroller 5 interacting with each other. The base station 4 of FIG. 2includes a base station control unit (BCU) 6, a transmission powerestimation unit (TRX) 7 and a radio channel unit (CHU) 8. Thefunctionalities provided by the respective units as well as thecontroller 5 are described in the following by using WCDMA terminology.It should, however, be appreciated that the following is only an exampleof the embodiments and thus the scope of the invention is not restrictedby the use of the WCDMA terminology, and that the invention can also beapplied to communication systems based on other standards.

The base station 4 of FIG. 2 includes a load control (LC) functionality10 controlling the outer loop power control functionality 12 of the basestation (OLPC/BS). The RNC 5 is shown to include a corresponding pair ofa load control functionality 11 and an outer loop power controlfunctionality (OLPC/RNC) 13. Communication paths or channels 14 and 15are provided between the respective LC and OLPC functionalities of theBS 4 and the RNC 5. The RNC is arranged to generate an Eb/No-setpoint 16which is subsequently transmitted to the BS in a outer loop powercontrol command 15. In the example the command is shown to be in theform of a relative “UP” or “DOWN” command, but the OLPC command from theRNC could also include an absolute value for the targeted Eb/No-setpointor a relative amount of increase or decrease of the setpoint value.

The OLPC/BS at the BS 4 receives the Eb/No-setpoint and may store thesetpoint in an appropriate storage functionality. The Eb/No-setpointwhich has been received from the RNC 5 is shown by a functionality 16 ofthe BS 4. For the purposes of clarity, the setpoint functionality of thebase station 4 is designated correspondingly with the setpointfunctionality 16 of the RNC 5.

In addition to the Eb/No-setpoint 16, the BS 4 of FIG. 2 is shown tocomprise a second or further Eb/No-setpoint or a BS Eb/No-setpointfunctionality 17. The arrangement is such that the second Eb/No-setpointfunctionality 17 is used for controlling the closed loop power controland/or uplink fast load control functionality 18 instead of a direct useof the Eb/No-setpoint 16 received from the RNC. The first Eb/No-setpoint16 of the BS 4 is always controlled by the RNC 5 and should always havethe same setpoint value as the setpoint 16 at the RNC 5. The secondEB/No-setpoint 17 is the setpoint actually provided to the closed loopfunctionality 18. The arrangement is such that in normal operation thesecond setpoint 17, i.e. OLPC/BS, follows the first setpoint, i.e.OLPC/RNC functionality 16.

When the quality of the bearer between the mobile station(s) in the celland the base station goes bad enough the outer loop PC functionality 13in the RNC (OLPC/RNC) 5 starts to increase the Eb/No-setpoints 16 of theradio link connection(s). An increase of the Eb/No-setpoints willeventually increase the uplink transmission powers from one or severalof the mobile stations in the cell correspondingly. Similarly, adecrease of the Eb/No-setpoints would decrease the transmission powers.

According to an embodiment of the invention the Load Control (LC)algorithm 10 at the base transceiver station (BS) 4 may start preventiveload control actions in order to avoid a situation in which mobilestations have to be “dropped” out i.e. disconnected from the cell. Forexample, the WCDMA Load Control (LC) algorithm 10 may set limit valuesfor the BS outer loop power control parameters or freeze the basestation (OLPC/BS) so that the OLPC/BS no longer follows Eb/No-setpointincrease commands by an outer loop power control 16 from the RNC 5(OLPC/RNC).

The limiting or freezing procedure of the setpoint or target value maybe initiated at the BS e.g. when a uplink total interference power level(PrxTotal) at the BS digital receiver exceeds a given threshold value.The total received wideband interference power (PrxTotal) is measured bythe base station BS on cell basis for Radio Resource Indication purposesin a per se known manner. This measurement is reported periodically tothe controller RNC, e.g. by using known NBAP/RADIO RESOURCE INDICATIONprocedure. The length of the period can be, for instance, selected froma range between 100 ms to 1 s. The RNC may then use the measurementresults for functionalities such as Admission Control (AC), Load Control(LC), and Packet Scheduler (PS) and so on.

The interference power level can be estimated by the TRX unit 7 of FIG.2. The threshold value for the interferece power is designated in thefollowing example by PrxTargetBS. The exemplifying threshold value isdefined by equation:PrxTargetBS=PrxTarget+PrxOffset,

-   -   wherein    -   PrxTarget is the planned target load of the system, and    -   PrxOffset is the allowed marginal above PrxTarget, after which        overload prevention actions are to be started.

When the total interference value PrxTotal in FIG. 2 exceeds PrxTargetBSthe OLPC/BS is frozen, and the BS 4 is no longer allowed to transmitclosed loop power control commands (CLPCs) towards the MS 1, even thoughthe BS 4 may still receive OLPCs from the RNC 5. According to a morespecific embodiment the outer loop PC functionality 18 in the BS(OLPC/BS) is frozen by the BS load control (BS LC) 10 after thePrxTargetBS is exceeded. In practice this means that the OLPC/BS ignoresany Eb/No-setpoint increase commands of the OLPC/RNC until the PrxTotalis below the exceeded threshold.

According to a preferred embodiment present in the flow chart of FIG. 7,the connection quality target value is not frozen to any precise valuein a power limitation situation, but instead the target used for theconnection control is prevented to exceed a certain predefined thresholdvalue. In other words, the power control mechanism is not switched offin a power limitation situation. Instead, the connection quality targetcan be changed and the transmission power levels adjusted in the cell aslong as the target does not exceed the temporary set upper limit.

According to one alternative only “DOWN” or “reduce target” type ofcommands are allowed in the closed loop while any commands aimed toincrease uplink transmission powers in the cell will not becometransmitted towards the mobile stations.

FIG. 2 presents in more detail the use of the PrxTotal measurement. Asmentioned above, OLPC/BS is frozen or a temporary upper limit is setwhen PrxTotal>PrxTargetBS. In the BS the OLPC/BS can be frozen orlimited on frame-bases, i.e. the determination of the PrxTotal can beaccomplished over each frame. In this case the total widebandinterference power received at the BS would be averaged over one radioframe (e.g. 10 ms) in the TRX-unit 7 of the BS 4, and reportedperiodically (e.g. every 10 ms) to the BCU unit 8 of the BS 4. PrxTotalcan then be calculated on 10 ms-cycles e.g. by using sliding averagewindow and an ALPHA-TRIMMED-MEAN filter or any other appropriate meansfor filtering.

The same applies to the OLPC/RNC, but it can be frozen or limited onlyafter a radio resource (RR) indication message 14 is received in the RNCload control 11. The RR indication can be sent e.g. every 0.1 s–1 s. Theouter loop PC can then be switched on/off based on monitoring of thereceived PrxTotal.

It is to be appreciated that the RNC 5 may alternatively receive someother type indication from the BS 4 instructing the RNC 5 to switch theOLPC/RNC on/off than the PrxTotal indication. It is also noted that thetotal interference value is only an example of the possible triggeringparameter, and other indications of a power limitation situation canalso be used for triggering the limitation or freezing procedure of theconnection quality setpoint at the base station and/or the controller.

As explained, the outer loop PC of the RNC (OLPC/RNC) can be limited orfrozen after the overload situation is indicated to the RNC even thoughthis is not always necessary. For instance, the arrangement can be suchthat the OLPC/RNC does not carry out any Eb/No-setpoint increases, butonly replaces “change” type indications with a “no change” typeindication. It is also possible to arrange the OLPC/RNC such that onlyEb/No-setpoint decreases are allowed. The RNC arrangement may also besuch that a temporary upper limit is set for the Eb/No-setpoint allowinga normal operation of the OLPC/RNC as long as the limit is not exceeded.The limit may equal or be different to that in use in the base station.If the limit is exceeded, use of any excessive setpoint values isprevented at the RNC and thus this embodiment corresponds the use of anupper limit at the BS.

It is also possible to have the outer loop functionality frozen orlimited such that all or a selected number of mobile stationscommunicating with the base station 4 are influenced, i.e. that thepower levels of all or selected connections are cut, frozen or heldbelow a certain limit. The connections may also be set into a priorityorder. In the latter instance the procedure can be such that the powerlevels of the lowest priority connections are limited and/or frozenfirst, and the highest priority connections are limited as last, if atall. The priority order classification of the connections may be basedon the type of the subscription. A possibility is to use the type of theongoing connection as basis for the prioritisation. For instance,speech, data and video connections may have different priorities. Thesame applies for “normal” calls, calls to emergency numbers, businesscalls, “hotline” calls and so on.

The OLPC/RNC freezing and/or limitation procedure may occur after theinterference level or some other indication of a power limitationsituation is signalled from the BS to the RNC. As explained, the RRindication message is sent periodically (e.g. in periods between 100 msto 1s). Now, if the interference value PrxTotal exceeds PrxTargetBS(=PrxTarget+PrxOffset) as discussed above, the OLPC/RNC can be limitedor frozen only after the indication of this has been received andprocessed at the RNC.

If the setpoint values at the BS are not allowed to follow the OLPC/RNCsfrom the RNC, the RNC Eb/No-setpoint 16 may start to differ from theEb/No-setpoint 17 used by the BS for the closed loop functionality 18.This is due the fact that in most cases there will be a delay before theRNC 5 receives the overload indication 14 from the BS 4 and thus beforethe RNC may take similar actions to the BS. In other words, if anoverload or another power limitation situation is detected, the twoEb/No-setpoints 16 and 17 of FIG. 2 start to drift because the outerloop PC generated by the RNC is no longer allowed to adjust the closedloop PC 18. This difference will be referred to in the following asdrifting.

After the power limitation situation is over, the operation of theOLPC/BS and OLPC/RNC is returned to a normal mode. The Eb/No-setpointdrifting between the BS and the RNC has to be removed during therecovery after the overload situation is over (PrxTotal<PrxTargetBS) andthe outer loop PC is again allowed to control the power levels. The basestation can remove the drift internally because it knows the actualsetpoint value 17 in at the base station 4 and also the setpoint value16 in use at the RNC 5. Thus it is possible to set either the setpointvalue 16 to equal with the actual setpoint 17 or vice versa before theoperation is returned to a normal mode. In addition, history informationcan be used for the recovery, i.e. the setpoint values in the BS and theRNC can be returned to a value used by them before the power limitationsituation was detected. It is also possible to use a default or nominalvalue to which the setpoint in the RNC and/or in the BS is returned atthe beginning of the normal mode.

However, in order to provide a controlled recovery and to avoid any too“sharp” changes in the setpoint values, it may be preferred that thereturning to the appropriate setpoint value is not done at once. This isespecially the case when the quality of the connection is substantiallybad. Therefore it may be preferred to use some procedure to graduallydecrease the drifting.

As shown by the flow chart of FIG. 8, the BS 4 may initiate the recoveryprocedure by checking for a possible drift of the Eb/No-setpoints whenan Eb/No-setpoint down command is received from the RNC 5. If the checkis positive, i.e. an existing drift is detected, the drifting is reducedinstead of the actual Eb/No-setpoint. When an Eb/No-setpoint up commandis received in BS, then the actual Eb/No-setpoint is always increased ifthe cell is not overloaded.

Before explaining in more detail the embodiments aimed for solving thedrifting problem, the arrangements of FIGS. 3 and 4 will be brieflydiscussed. It is noted that even though FIGS. 3 and 4 disclose a morecomplex communication network arrangement than FIG. 2, the followingembodiments can also be implemented in the FIG. 2 implementation.

FIG. 3 shows a situation in which a mobile station MS is controlled bytwo separate base stations 4 and 4′ (e.g. during a handover procedure).A1 and A2 designate the first setpoints corresponding the setpoint 16 ofFIG. 2 in the respective base stations. The second setpoint of the basestations is correspondingly designated by B1 and B2. The RNC 5 controlsEB/No-setpoints of the base stations 4 and 4′ by providing both basestations with relative outer loop power control (UP/DOWN) over anexemplifying Iub interface 19.

FIG. 4 shows an embodiment in which the mobile station is subjected to asoft handover procedure. As in the above, the outer loop PC of a radionetwork controller can control several Eb/No-setpoints in several BSs.However, FIG. 4 discloses the possibility that all Eb/No-setpoints in aBS are not controlled by the same controller. In this kind of situationone of the controllers is the main controller while the other controlleris used for assisting in the control of the station during the handoverproceedings. In FIG. 4 the main controller comprises a servingRNC(S—RNC) 5 and the assisting controller comprises a drifting RNC(D-RNC) 5′. The serving and drifting RNC are connected to each otherover an exemplifying Iur interface 20. Since the overload indication hasnow to be transmitted from the BS1 to the serving RNC 5 over twointerfaces 19 and 20 and also through the drifting RNC 5′, the delay iseven longer than what it would be in FIG. 2 or 3.

The serving RNC 5 of FIG. 4 controls the outer loop PC. However, theload control is performed by the load control 11 of the drifting RNC 5′.This means that in the case of a power limitation situation (overload atBS1 in FIG. 4), the outer loop PC functionality performed by the servingRNC is not interrupted, and thus the used Eb/No-setpoint (B1) andEb/No-setpoint of RNC (A,A1) start to drift. Moreover, theEb/No-setpoints (A2,B2) used for other handover branches can also startto increase. However, this does not cause uplink (UL) power increase aslong as BS1 can control power of MS in addition to BS2. The reason forthis is that the MS will not increase its transmission power as long asit receives at least one DOWN command from at least one base station.

In a normal situation A1 A2 A and B1 A1 and B2 A2 in FIGS. 3 and 4.Because of the overload at the BS1 the Eb/No-setpoints have started todrift. The controlling RNC allows the system to return to the normal PCfunctionality after the radio resource indication measurements haveindicated that the PrxTotal is below the set PrxTargetBS. After the cellhas returned back on the normal load state (PrxTotal<PrxTargetBS) theouter loop PC is allowed again to control the power levels at the BS. Atthis stage a drifting detection unit 21 can define the amount of thedrifting.

When the normal operation of the power control functionality is allowedagain, the drifting of the Eb/No-setpoints has to be reduced. Basestation BS1 can remove the drift (A1< >B1, A2< >B2) internally, becauseit knows the actual used value (B1,B2) and also the value in use in theRNC (A1,A2). However, in order to avoid any too sharp changes in thesetpoint values, a gradual Eb/No-setpoint adjustment can beaccomplished. This can be done e.g. such that when an Eb/No-setpointdown command is received from the RNC 5, the BS checks drift ofEb/No-setpoints. If the check is positive the drift is reduced insteadof the actual Eb/No-setpoint. When an Eb/No-setpoint up command isreceived in BS, then the actual Eb/No-setpoint is always increased ifthe cell is not overloaded.

Table 1 of FIG. 5 shows various stages of the embodiment for reducing adrift of Eb/No-setpoints between a BS and a RNC when using the followingparameters.

SetUp = 0.5 dB StepDown = 0.1 dB Initial Eb/No-setpoint = 4.1 dB

It is noted that Table 1 shows the operation of an exemplifying powercontrol mechanism using relative adjustments. However, the hereindescribed principles can also be applied to a power control mechanismusing absolute adjustment of the power levels.

In Table 1 “A” is the Eb/No-setpoint of the RNC. “A1” and “A2” are theouter loop PC Eb/No-setpoint values of BS1 and BS2, respectively. BS1and BS2 are both controlled by the same RNC. “B1” and “B2” are theEb/No-setpoints used by the closed loop PC. “B1” and B2” are controlledby the outer loop PC of the BS. “OFF” means that the outer loop PCfunctionality is switched off. In other words, when the OLPC is in “OFF”state, the adjustment of “B1” and “B2” is not allowed in base stationsregardless the commands transmitted by the OLPC. Correspondingly,adjustment of the “A1” and “A2” values is not allowed in the RNC. Whenthe OLPC is switched “ON”, this means that outer loop PC functionalityis allowed again.

As explained, the OLPC/BS at the base station of the overloaded cell isfrozen before the OLPC/RNC at the RNC becomes frozen and therefore anEb/No-setpoint drifting may exist between the outer loops of the basestation 4 and the radio network controller 5. Although the drifting canbe eliminated by using the algorithm described above, this may not befast enough procedure in all occasions and some further processing maybe required.

For instance, the OLPC/RNC might already have been escalated/diverged,i.e. the Eb/No-setpoint of the OLPC/RNC may have raised substantially(several dBs) during the last RR indication period. This is causedpartially because the RR indication period (i.e. how often the RRindications are sent) may be substantially long, wherein the OLPC/RNCwill be frozen a long time (up to one RR indication period) after theOLPC/BS of the overloaded cell was frozen. The freezing of the OLPC/BSmay, however, have lead into a generation of numerous frame errors (FE).The frame errors will increase the FER. The increased FER will thenfurther unnecessarily increase the Eb/No-setpoint of the OLPC/RNC, andthis will increase further the drifting between the OLPC/BS and theOLPC/RNC.

The above phenomena is one of the reasons why the normal functionalityof the OLPC/RNC may not be enough right after the power limitationsituation is over and the limiting or freezing of the OLPC/BS andOLPC/RNC is cancelled. The OLPC/RNC Eb/No-setpoint may have been driftedseveral dBs above the situation the Eb/No-setpoint was during theprevious RR indication period just before the power limitation isencountered in the RNC by a new RR indication message from the BS. TheOLPC/RNC drift can be defined in the following manner:OLPC/RNC DRIFT=Eb/NO ₂ — Eb/NO ₁

-   -   where    -   Eb/NO₂ is the Eb/No-setpoint at the point when the overload        situation is over and the OLPC/RNC is no longer frozen; and    -   Eb/NO₁ is the last Eb/No-setpoint of a RR indication period        preceding the RR indication sent from the overloaded BS.

The example presented in Table 2 of FIG. 6 will clarify further theembodiment. In Table 2 Eb/No1 is the last Eb/No-setpoint of the previousRR indication period preceeding the RR indication sent from theoverloaded BS. EB/No2 is the Eb/No-setpoint at the point of time whenthe overload situation is over and the OLPC/RNC is no longer frozen. “A”is the Eb/No-setpoint of the RNC. “A1” and “A2” are the outer loop PCEb/No-setpoint values of the BS, which are controlled by the RNC. “B1”and “B2” are the Eb/No-setpoints used by the closed loop PC, and arecontrolled by the outer loop PC of BS (OLPC/BS). “OFF” means that theouter loop PC functionality is switched off (i.e. adjusting of “B1” and“B2” is not allowed in the BS or in the case of the RNC, adjusting of“A1” and “A2” values is not allowed. “ON” means that the outer loop PCfunctionality is allowed to return to normal operation.

It is possible that the base station and the controller have estimated adifferent amount of drift to be removed, e.g. due to the different timeof initiating the limitation/freezing procedures. Therefore thealgorithm cab be such that after the OLPC/RNC is freed, the drift(=EbNo2−EbNo1) will be eliminated by decreasing the OLPC/RNCEb/No-setpoint e.g. by 0.2 dB (normal decrease may be e.g. 0.1 dB) untilthe drift equals zero or a new Frame Error occurs. At this stage thedrift elimination algorithm at the RNC is cancelled, the Eb/No-setpointis increased by e.g. 0.5 dB and a normal OLPC/RNC action will follow.However, the OLPC/BS drifting prevention algorithm described above maystill operate until the drift thereof is removed in its entirety.

It should be appreciated that whilst embodiments of the presentinvention have been described in relation to mobile stations,embodiments of the present invention are applicable to any othersuitable type of user equipment.

The data is described as being in packet form. In alternativeembodiments of the invention the data may be sent in any suitableformat.

The embodiment of the present invention has been described in thecontext of a CDMA system. This invention is also applicable to any otheraccess techniques including frequency division multiple access or timedivision multiple access as well as any hybrids thereof.

The embodiment of the invention has discussed the interaction between aradio network controller and a base station. Embodiments of the presentinvention can be applicable to other network elements where applicable.

It is also noted herein that while the above describes one exemplifyingembodiment of the invention, there are several variations andmodifications which may be made to the disclosed solution withoutdeparting from the scope of the present invention as defined in theappended claims.

1. A method in a communication system, said system comprising acontroller and a first station for communication with a second stationwith variable transmission power over a radio connection, wherein thecontroller provides the first station with a target for a transmissionparameter of the radio connection and the first station adjusts thetransmission power of the second station on basis of the target,comprising: monitoring for a predefined condition; upon occurrence ofthe predefined condition, preventing use of a target for thetransmission parameter exceeding a limit value for the target for thetransmission parameters; receiving the target for the transmissionparameter from the controller at the first station; and creating afurther target for the transmission parameter at the first station foruse in the transmission power adjustment, wherein the further targetcorresponds to the target received from the controller until thepredefined condition is detected whereafter the further target isprevented to exceed the limit value for the target and the targetreceived from the controller is ignored.
 2. A method according to claim1, wherein use of a target for the transmission parameter exceeding thelimit value is prevented at the first station.
 3. A method according toclaim 1, wherein use of a target for the transmission parameterexceeding the limit value is prevented at the controller.
 4. A methodaccording to any of the preceding claims, wherein the limit value equalswith the target for the transmission parameter in use at the moment ofdetecting the predefined condition.
 5. A method according to claim 4,wherein the target for the transmission parameter is held at the limitvalue until the condition is over.
 6. A method according to claim 1,wherein the predefined condition comprises a temporary power limitationsituation at the first station.
 7. A method according to claim 1,wherein the predefined condition comprises an overload situation at thefirst station.
 8. A method according to claim 1, wherein the predefinedcondition comprises a failure in the communication system.
 9. A methodaccording to claim 1, wherein the monitoring of the occurrence of thepredefined condition is based on determination of the interference powerof the radio connection.
 10. A method in according to claim 1, whereinthe target for the transmission parameter comprises connection qualitytarget.
 11. A method according to claim 1, wherein the target for thetransmission parameter comprises signalling energy/noise target.
 12. Amethod according to claim 1, wherein the target for the transmissionparameter comprises a target transmission power level of thetransmission from the second station.
 13. A method according to claim 1,wherein the step of preventing the target for the transmission parameterto exceed the limit value comprises ignoring power control commands atthe first station until the predefined condition is over.
 14. A methodaccording to claim 1, wherein the step of preventing of the target forthe transmission parameter to exceed the predefined value comprisespreventing a generation of new power control commands at the controlleruntil the predefined condition is over.
 15. A method according to claim1, wherein the controller controls the transmission powers between thefirst station and the second station by means of outer loop powercontrol.
 16. A method in accordance with claim 1, further comprisingsteps of: detecting a difference between the value of the target for thetransmission parameter provided by the controller and the value of thetarget for the transmission parameter used for power control by thefirst station after the predefined condition is over; and reducing thedifference between the said two target values.
 17. A method according toclaim 16, wherein reducing of the difference is based on historyinformation of the target used for the power control prior the detectionof the condition.
 18. A method according to claim 16, wherein the stepof reducing the difference comprises changing the value of the targetprovided by the controller to equal values of the target used by thefirst station for controlling the transmission power at the moment thecondition is detected to be over.
 19. A method according to claim 16,wherein the difference between the said two target values is reducedgradually.
 20. A method according to claim 19, wherein the gradualreducing of the difference comprises steps of; ignoring a request fromthe controller to reduce the transmission power until the differencebetween the target values used by the first station and provided by thecontroller is below a predefined level; and subtracting a predefinedamount from the difference as response to said request.
 21. A methodaccording to claim 20, wherein the predefined amount corresponds therequested decrease of the transmission power.
 22. A method according toclaim 19, wherein the gradual reducing of the difference comprisesrequesting a decrease of the transmission power by an amount that isgreater than the amount of decrease requested in a normal mode ofoperation until the difference between the target values used by thefirst station and provided by the controller is below a predefinedlevel.
 23. A method according to claim 1, wherein the transmission powercontrol is based on use of relative power control requests.
 24. A methodaccording to claim 1, wherein the communication system comprises afurther station similar to the first station and the controller controlsthe transmission power of the second station by providing both the firstand the further station with targets for the transmission parameter. 25.A method according to claim 1, wherein connections between the firststation and other stations are adjusted in a priority order.
 26. Amethod according to claim 1, wherein the controller comprises a radionetwork controller of a cellular communication system, the first stationcomprises a base station of the cellular communication system and thesecond station comprises a mobile station, and wherein the transmissionpower to be adjusted comprises transmission power from at least onemobile station towards at least one base station.
 27. A communicationsystem comprising: a controller arranged to control transmission powerof stations; a first station and a second station capable of providing acommunication path therebetween, wherein the controller is arranged toprovide the first station with a target for use in control of thetransmission power of the second station; monitoring means formonitoring for a predefined condition; and means for preventing use of atarget for the transmission parameter exceeding a limit value for thetarget for the transmission parameter upon occurrence of the predefinedcondition, the first station comprising a first target functionality forreceiving the target from the controller and a further targetfunctionality for generating a further target for the transmissionparameter, wherein the arrangement is such that the further target isused for the power control of the second station and corresponds to thetarget provided by the controller unless the predefined condition isdetected whereafter the further target is set such that the limit valuefor the target for the transmission parameter is not exceeded.
 28. Acommunication system according to claim 27, further comprising detectingmeans for detecting a difference between the target and the furthertarget and recovery means for reducing the difference after thepredefined condition is over.
 29. A communication system according toclaim 28, wherein the recovery means are arranged to reduce thedifference gradually.
 30. A communication system according to claim 27,wherein the controller comprises a radio network controller of acellular communication system, the first station comprises a basestation of the cellular communication system and the second stationcomprises a mobile station, and wherein the transmission power to beadjusted comprises transmission power from at least one mobile stationtowards at least one base station.
 31. A station of a communicationsystem, said station controlling transmission power of a further stationtransmitting towards the station, wherein the station is arranged to:receive a target for a transmission parameter provided by a controllerof the communications system for use in the control of transmissionpower of the further station; monitor for a predefined condition; andupon occurrence of the predefined condition, to prevent use of targetsfor the transmission parameter exceeding a limit value for the targetfor the transmission parameter, said station further comprising a firsttarget functionality for receiving the target for the transmissionparameter provided by the controller and a further target functionalityfor generating a further target for the transmission parameter, whereinthe arrangement is such that the further target is used for the powercontrol of the further station and corresponds to the target receivedfrom the controller unless the predefined condition is detectedwhereafter the further target is set by the further target functionalitysuch that the limit value for the target is not exceeded.
 32. A stationaccording to claim 31, further comprising detecting means for detectinga difference between the target and the further target and recoverymeans for reducing the difference after the predefined condition isover.
 33. A station according to claim 32, wherein the recovery meansare arranged to reduce the difference gradually.